A053245 Numbers k such that both A053238(k) and A053238(k+1) = 1.

20, 49, 56, 79, 108, 132, 145, 170, 177, 230, 253, 277, 289, 307, 347, 382, 405, 412, 424, 437, 495, 548, 585, 592, 633, 645, 704, 734, 752, 764, 789, 802, 841, 854, 930, 943, 967, 974, 1005, 1012, 1053, 1066, 1130, 1154, 1179, 1186, 1216, 1223, 1264

Offset: 1

Author

Asher Auel, Jan 10 2000

Keywords

• nonn

Comments

Pairs of consecutive 1's occur uncommonly often in A053238.

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A053226, A053238, A053239, A053240, A053241, A053242, A053243, A053244.

Programs

Haskell

a053245 n = a053245_list !! (n-1)
a053245_list = f a053242_list where
   f (x:x':xs) | x' == x+1 = x : f xs
               | otherwise = f (x':xs)
-- Reinhard Zumkeller, Oct 16 2011

Maple

with(numtheory): f := [seq( `if`((sigma(i) > sigma(i+1)),i,print( )), i=1..5000)];
seq(`if`((f[i+2]-f[i+1]=1) and (f[i+1]-f[i]=1),i,print( )), i=1..1500);